1. Mole Problems

2. Calculating molar mass
Round all masses to the 10ths place

3. Calculate the molecular weight of Fe2O3
Step One: two atoms of iron and three of oxygen
Step Two: Fe = 55.8 amu and O = 16.0 amu
Step Three: (2 x 55.8) + (3 x 16.0)
Step Four: = amu (grams) for one mole

4. Calculate the molecular weight of KClO4
Step One: one atom of potassium, one of chlorine, and four of oxygen.
Step Two: K = 39.1 amu, Cl = 35.5 amu, O = amu
Step Three: (1 x 39.1) + (1 x 35.5) + (4 x 16.0)
Step Four: = amu (grams) for one mole

5. Calculate the molecular weight of (NH4)2S
Step One: two atoms of nitrogen, eight of hydrogen and one of sulfur
Step Two: N = 14.0 amu, H = 1.0 amu, S = 32.1 amu
Step Three: (2 x 14.0) + (8 x 1.0) + (1 x 32.1)
Step Four: = 68.1 amu (grams) for one mole

6. Calculate the molar mass of Al(NO3)3
Al(1 x 27.0) + N(3 x 14.0) + O(9 x 16.0) =
213.0 amu (grams) is the mass of one mole of aluminum nitrate.

7. You Try These… 1. AlCl3 2. Ba(SCN)2 3. LiH 4. Ba(BrO3)2 5. AlBr3
6. HCl

8. Answers 1. 133.5 g/mol 2. 253.5 g/mol 3. 7.9 g/mol 4. 393.1 g/mol

9. Round all final answers to 3 sig figs
GRAMS to MOLES
Round all final answers to 3 sig figs

10. Convert 25.0 grams of KMnO4 to moles.
KMnO4 = g / mole of KMnO4
Now let’s solve it
25.0 g x 1 mole = moles
158.0 g
0.158 moles

11. Calculate how many moles are in 17.0 grams of H2O2.
H2O2 = 34.0 g / mole
Now, let’s solve it
17.0 g x 1 mol H2O2 = 0.5 moles
34.0 g
0.500 moles

12. You try these… Calculate the moles present in: 1) 2.00 grams of H2O
2) grams of KBr
3) 100. grams of KClO4
4) 8.76 grams of NaOH
5) grams of Na2CO3
Remember to round answers to 3 sig figs

13. Answers 1) 0.111 moles 2) 0.635 moles 3) 0.722 moles 4) 0.219 moles

14. Round all answers to 3 sig figs
MOLES TO GRAMS
Round all answers to 3 sig figs

15. Calculate how many grams are in 0.700 moles of H2O2
H2O2 molar mass = 34.0 grams/mole
0.700 moles x 34.0 grams = 23.8 g
1 mole
23.8 grams

16. Convert 2.50 moles of KClO3 to grams.
KClO3 molecular mass = g/mole
2.50 moles x g = grams
1 mole
307 grams

17. You try these… Calculate the grams present in: 1) 0.200 moles of H2S
2) moles of KI
3) moles of KClO
4) moles of NaOH
5) x 10-5 moles of Na2CO3
Remember to round answer to 3 sig figs

18. Answers 1) 6.82 grams 2) 16.6 grams 3) 136 grams 4) 30.0 grams

19. 6.02 x 1023 particles = 1 mole Particles can mean atoms or molecules
Avogadro's Number
6.02 x 1023 particles = 1 mole
Particles can mean atoms or molecules

20. One mole of ANY specified entity contains 6.02 x 1023 of that entity

21. For Example One mole of donuts contains 6.02 x 1023 donuts
One mole of H2O contains 6.02 x molecules
One mole of nails contains 6.02 x 1023 nails
One mole of Fe contains 6.02 x 1023 atoms

22. Continued One mole of dogs contains 6.02 x 1023 dogs
One mole of electrons contains 6.02 x electrons
One mole of Chemistry students contains x 1023 poor, suffering (I mean happy, joyful) high school students

23. 0.450 mole of Fe contains how many atoms?
0.450 mole Fe x 6.02 x 1023 atoms
1 mole
= 2.709x1023 atoms
Final, rounded answer: 2.71x1023 atoms

24. 0.200 mole of H2O contains how many molecules?
0.200 mole x 6.02 x 1023 atoms
1 mole
= 1.204x1023 atoms
Final, rounded answer: 1.20x1023 atoms

25. You try these…
1) Calculate the number of molecules in mole of H2O
2) Calculate the number of atoms in mole of Fe
Remember to round to 3 sig figs

26. Answers
1) 6.37x1023 molecules
2) 4.52x1023 atoms

27. Two Step Problems Grams to particles OR particles to grams
Grams to atoms OR atoms to grams
If MOLE is not stated, it’s a two step problem
ROUND ALL ANSWERS TO # SIG FIGS

28. 0.450 gram of Fe contains how many atoms?
0.450 g x 1 mole Fe x 6.02x1023 atoms =
55.8 g mole
x1021 atoms
Final answer = 4.85x1021 atoms

29. 0.200 gram of H2O contains how many molecules?
H2O molecular mass = 18.0 g
0.200 g x 1 mole H2O x 6.02x1023 molecules
18.0 g mole
x1021 molecules
Final answer = 6.68x1021 molecules

30. You try these…
1) Calculate the number of molecules in gram of H2O
2) Calculate the number of atoms in gram of Fe
Remember to round answer to 3 sig figs

31. Answers
1) 3.54x1022 molecules
2) 8.10x1021 atoms

32. THE END